In conventional web conveyance processes, conveyed web is exposed to various treatment protocols. These processes most typically include rollers to support the web and in some cases involve tenters to transport the web by restraining the edges.
In cases where the web is not stiff, rollers have been used to support the web. This method is inexpensive, but does not address concerns with web defect generation related to the roller contact. Defects such as scratches, surface replication/adhesion, and impressions are generated with roller contact in this method. In addition, wrap on the rollers does little to restrain the web in cases where web shrinkage due to applied tension is a concern. A variation of the roller supported conveyance is air conveyance. In this process, the web is supported by either air blown from plenums or air blown through porous rollers (as taught in Japanese Kokai Sho 55[1980]-135046). Air conveyance is disadvantaged where the web is susceptible to distortion from the air streams.
In cases where web defects and/or shrinkage is a concern, tenters have been used to avoid roller contact and provide widthwise restraint or orientation. Tenters are complex pieces of equipment with large potential for dirt generation and high installed costs. Tenters can also damage the edges where the edge of the web is fragile. Nakajima and Ono demonstrated a process for tentering sensitive webs in Japanese Kokoku HEI 5[1993]-19898. This technology is expensive and creates dirt by perforating the web edge to constrain it.
Therefore, there persists a need in the art for an apparatus that conveys web of indeterminate length that prevents the conveyed web from shrinking during processing while not damaging sensitive webs.